net: udp: Add support for getsockopt(..., ..., UDP_GRO, ..., ...);

[ Upstream commit 9818461 ]

Support for UDP_GRO was added in the past but the implementation for
getsockopt was missed which did lead to an error when we tried to
retrieve the setting for UDP_GRO. This patch adds the missing switch
case for UDP_GRO

Fixes: e20cf8d ("udp: implement GRO for plain UDP sockets.")
Signed-off-by: Norman Maurer <norman_maurer@apple.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/ipv4/udp.c

@@ -2747,6 +2747,10 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 		val = up->gso_size;
 		break;
 
+	case UDP_GRO:
+		val = up->gro_enabled;
+		break;
+
 	/* The following two cannot be changed on UDP sockets, the return is
 	 * always 0 (which corresponds to the full checksum coverage of UDP). */
 	case UDPLITE_SEND_CSCOV: